Electronic devices exchange interface signals; each interface signal carries digital data, so the electronic devices can establish communications of messages and information. When a transmitting electronic device sends digital data to a receiving electronic device, the transmitting electronic device serializes data bits of the digital data in an interface signal based on a data clock, and transmits the interface signal to the receiving electronic device. As the interface signal is received, the receiving electronic device needs to perform data extraction for the interface signal, thus each data bit of the interface signal can be retrieved, and the messages and information in the digital data of the transmitting electronic device are recovered.
For different electronic devices to correctly exchange data, digital data are carried by an interface signal according to a predetermined interface protocol/specification, such as various versions of the universal serial bus (USB) specification, the serial advance technology attachment (SATA) specification and the peripheral component interconnect express (PCI-E) specification, etc. In modern interface specification, digital data are packed into packets, and the packet forms a basic unit for data exchange. However, in modern interface specification, the data clock is not transmitted to the receiving electronic device along with the interface signal. The receiving electronic device must extract each data bit without the data clock.
For demands of data extraction, a prior art, such as the one mentioned in U.S. Pat. No. 5,799,050, utilizes crystal oscillator to provide a precise clock and accordingly performs data extraction. However, because crystal oscillators can not be integrated into dice of integrated circuits, a die needs additional pins to receive the clock of the crystal oscillator, thus cost and power consumption of the prior art are increased.
In another kind of prior arts, such as those mentioned in U.S. Pat. Nos. 7,453,958 and 6,407,641, a rough clock close to the data clock is first provided, then it is fine-tuned to be closer to the data clock. However, this kind of prior arts is sensitive to variations of (manufacturing) process, (supply) voltage and (operation) temperature. If the rough clock is far away from the data clock, it is difficult, or time-consuming, to fine-tune the rough clock to approximate the data clock. In addition, this kind of prior art lacks application flexibility, since a same data extraction design does not apply to different interface specifications. Because different interface specifications adopt clocks of different rates and packets of different lengths, demanded clock precisions for data extraction are also different. For example, as packet is longer (contains more data bits), the clock used for data extraction needs to be more precise. Therefore, a same fine-tuning mechanism can not apply to interfaces of different interface specifications.